(a) Field of the Invention
The present invention relates to a mobile relay station (or a relay, a repeater, or the like) and a handover method thereof.
(b) Description of the Related Art
In a wireless communication system environment, a mobile relay station establishes a relay link with a superordinate base station and serves to relay data from subordinate terminals to the superordinate base station through the relay link.
When signal quality of the superordinate base station, establishing the relay link with the mobile relay station, is degraded while signal quality of a neighbor base station is increased, the mobile relay station performs handover to the neighbor base station.
3rd wireless communication international standards such as existing IEEE 802.16j define techniques in consideration of even a mobile relay station as well as a fixed type relay station, in which, thus, methods and procedures with respect to handover of relay stations are defined. However, 4th wireless communication international standards such as IEEE 802.16m define techniques in consideration of only fixed type relay stations, without defining handover methods and procedures of mobile relay stations.
Meanwhile, in the existing handover method and procedure of a mobile relay station, there is a service interruption period due to handover of a mobile relay station, and due to the service interruption period, subordinate terminals may perform handover twice. During the service interruption period due to handover of a mobile relay station, subordinate terminals may determine that they are not within service coverage of a serving relay station to which the subordinate terminals are connected, so they attempt handover to a different relay station or a base station. After the handover of the mobile relay station to a neighbor base station is completed, the subordinate terminals perform handover again to the mobile relay station (i.e., the previous serving relay station).